Mechanism for retracting and automatically locking undercarriages of aircraft



June 17, 1947. J MARTlN- 2,422,576 MECHANISM FOR RETRACTING ANDAUTOMATICALLY v LOCKING UNDERCARRIAGES OF AIRCRAFT Filed June 25, 1943 2Sheets-Sheet 1' J. MARTIN MECHANISM FOR RETRACTING AND AUTOMATICALLYLOCKING UNDERCARRIAGES OF AIRCRAFT June 17, 1947.

2 Sheets-Sheet 2 Filed June 25, 1943 N GEN R Patented June 17, 1947MECHANISM FOR RETRACTING AND AUTO- MATICALLY LOCKING UNDERCARRIAGES FAIRCRAFT James Martin, Higher Denham, near Uxbridge, England ApplicationJune 25, 1943, Serial No; 492,286 In Great Britain July 15, 1942 Thisinvention relates to improved means for automatically locking andstrutting oleo or other resilient legs of aircraft undercarriages in theoperative position and for collapsing or folding such locking andstrutting means into a compact space in close proximity to the folded orraised legs, and the chief object of the invention is to provide a quickaction lowering mechanism which is positive in its locking operation andis gravity and spring operated so as to obviate the necessity ofcomplicated driving mechanism. Another object of this invention is toprovide an improved collapsible radius rod or strut incorporating meansto automatically lock the oleo leg or the like in the operative positionand to automatically unlock the leg to release it for 1 Claim. (Cl.244-102) raising 0r folding as soon as driving means is set intooperation to raise or fold the leg.

According to this invention an oleo, or oleo pneumatic type ofundercarriage or other suitable shock absorbing undercarriage foraircraft has its wheel carrying leg strutted in the lowered or operativeposition by a radius rod comprising two arms hinged together at adjacentends by a knuckle joint so that they may be abutted end to endsubstantially in coaxial alignment in the strutting position and foldedtowards each other when retracting the undercarriage, one of said armsbeing adapted to be pivoted at its end remote from the knuckle joint tothe leg, and the other arm being adapted to be pivoted to the aircraft,means provided with said arms in juxtaposition to said knuckle joint toautomatically lock the two arms rigidly together when they are moved tothe substantially coaxial relationship, spring means urging said arms tothe leg strutting position when the two arms have been moved apartthrough a predetermined angle, said spring means yieldingly opposingsaid movement apart of the arms through said angle, the said lockingmeans being adapted to be connected for unlocking operation to the meansfor retracting the leg to the folded away position.

In the preferred form of the present invention, the said radius rodconsists of two arms united by a knuckle joint so that they may befolded close together in the inoperative position, means being providedwith theknuckle joint to lock the two arms in substantially co-axialalignment when the leg is lowered, spring means to positively force thetwo arms into fully extended or operative relationship following apredetermined movement of the leg by gravity and remote control operatedmeans to release the lock and to pull the leg to the raised position.

In order that this invention may be clearly understood and readilycarried into effect draw,- ings are appended hereto illustrating anembodiment thereof, and wherein,

, Fig. 1 is a broken front elevation view showing the undercarriageretracted,

Fig. 2 is a broken front elevation view showing the undercarriagelowered to an extent in which tie rods hereinafter described form a deadcentre position with the axis of a knuckle joint pivotally connectingtwo arms of the radius rod,

Fig. 3 is a broken front elevation view showing the undercarriage fullylowered,

Fig. 4 is a view of the extended tie rod taken in the direction of thearrow ll of Fig. 3.

Fig. 5 is a longitudinal sectional side elevation of Fig. 4, and

Fig. 6 is an outside side elevation view of Fig. 4.

Referring to the drawings the cylinder l of oleo leg I is pivoted at oneend to the appropriate part of the aircraft 2 by a bolt and suitablebearings indicated generally by the reference numeral 3, and the legcarries the wheel 4 at its end remote from its pivot 3 in well knownmanner.

The leg I is adapted to be raised by the tene sion of a cable 5connectedat one end to suitable winding or driving mechanism inside theaircraft and anchored at its other end to theleg in a manner hereinafterexplained through the medium of a collapsible radius rod constituted bytwo arms 6 and 1 connected together by a knuckle joint 8. The initial."retracting or lifting tension on the cable 5 is arranged to disengagea locking catch member 9 (see Fig. 4) as hereinafter described and thento relieve the knuckle joint of the influence of a coiled com pressionspring H] which normally functions to force the arms 8 and T of theradius rod into coaxial relationship and to maintain them in the fullystrutting position. When the knuckle joint is relieved of the influenceof the spring lit, the joint may be readily broken to allow the arms tofold and the undercarriage to be raised.

The arm I of the radius rod is pivoted at one end by a lug I thereon to'a bifurcated lug II on the outer end of the cylinder l of the leg,andthe relatively remote end of the other arm 6 is fixed to an outerring of a ball bearing I2 located on a fixed pivot pin it in a bracketl4 fixed to the appropriate part of the aeroplane wing or fuselage.These two arms 6 and l are both mainly of tubular section and areco-axial when the under-carriage is down. The lower of these two arms ofthe radius rod, 1. e. the arm I pivoted to the cylinder of the leg,accommodates at its knuckle joint end a spring loaded locking plunger I5 shaped at one end to form the said catch 9, such catch being adaptedto trip into a recess I6 (see Fig. 5) in the free end of the upper arm6, for which purpose such free end is camshaped as at 11 to enable thecatch end 9 of the plunger l5 to slide thereover until it trips into thesaid recess. This plunger I5 slides concentrically in a tubular housing18 screwed into the inner end of the tubular arm 7, a plug or annularretaining nut l9 being threaded into the end of such housin inside thisarm to form an abutment for one end of a coiled compression spring 20encircling the plunger and abutting at its other end against an annularstop E5 on the plunger. This housing [8 is bored axially at its endnearer the knuckle joint to slidably accommodate the exposed or catchend 9 of the plunger I5, such catch end of the plunger being tapered andradiused at its corners as shown in Fig. 5, to engage smoothly in thecorrespondingly tapered recess 16 of the said camshaped end I! of theupper arm 6 of the radius rod. The housing I8 is bifurcated at one endas at Hi to form part of the knuckle joint of the radius rod, the otherpart, being the said camshaped end 11 of the upper arm, a hinge pin 8being passed through such lugs and the said end of the upper arm, theaxis of this hinge pin being offset in relation to the' axis of theextended radius rod.

A sleeve 2| loose on the inner end of the lower arm 1 of the radius rodabuts against a flange I thereon, the other end of this sleeve beingflanged as at 21 to form an abutment for the inner end of a stout coiledcompression spring comprising the beforesaid spring l0 encircling thelower arm I and which positively. forces the two arms of the radius rodinto the fully extended position or co-axial relationship. The other endof this sprin abuts against a flange 22"- on a thrust collar 22 cuppedto encircle this end of the spring and carried by a sleeve 23 havingfreedom for limited sliding movement upon the said lowerarm. The thrustcollar is connected by a pair of slotted tie rods 24 to a pair of forkends .25 on the upper arm 6 which project beyond the pivot (hinge pin 8of the offset knuckle joint; The slots in the tie rods 24 are indicatedby the reference numeral 24 and they receive studs 25 of the fork ends25. The sprin thus exerts a strong influence on the knuckle joint toensure the completion of movement of the two arms into the fullyextended coaxial position. In order to break the knuckle joint of theradius rod when it is desired to retract the undercarriage the lockingplunger l5 with its catch '9 has to be retracted and this spring l0slightly compressed so that the slotted tie rods 24 no longer transmitits force to the fork ends 25 of the upper arm 6 of the radius rod andthe knuckle joint is relieved of the influence of the spring.

This latter dual operation is eifected by the initial pull on theoperating cable 5 and for this purpose the locking plunger I5 isconnected inside the arm 1 by a push rod 26 to one end of a small lever2 pivoted by a bolt 28 to and between a pair of lugs 29 formed on thesaid sleeve 23 carrying the said thrust collar. The outer end of thislever has pinned to it by a pivot bolt 30 one end of a bush or thimble3l in which is fixed the appropriate end of the said cable 5 so that theinitial operative pull of the cable '5 turns the lever 21 of the lockingplunger push rod 26 slightly on a fulcrum afforded by its pivotalconnection to the sleeve 23 thus withdrawing the catch end of thelocking plunger [5 and unlocking the knuckle joint. When the inner endof the small lever 21 abuts against the closed end of the arm 1 as shownin broken lines in Fig. 5, then the small lever turns about this closedend as a fulcrum and further pull on the cable will move the thrustcollar 22 to compress the spring in on the lower arm 1. Owing to the10st motion in the slotted connection of the tie rods 24 to the arm 6the force exerted by the spring is no longer communicated to the forkends 25 of the upper arm of the radius rod and the knuckle joint iseasily broken. Further pull on the cable 5 folds up the two arms 6 and 1of the radius rod and raises the leg of the undercarriage.

The axis of the pivot bolt 8 of the knuckle joint 8 of the two arms 6and l of the radius rod is, as beforesaid, uni-lateral in relation tothe axis of the extended radius rod and is slightly above the commonaxis of the two studs 25 engaged in the said slots 24 of the tie rods,the relative positions of these axes being such that when the leg hasdropped about 25 the two tie rods are in a dead-centre position inrelation'to such axes as shown in Fig. 2. As soon as the dead-centreposition is passed, the force exerted by the compression spring l0,through the tie rods 24, acts to turn the two arms 6 and 7 of the radiusrod about the knuckle joint pivot bolt I3 until the knuckle joint snapsforcibly into the straight position and is locked by the locking catch9. In this position the leg is fully down and is locked and braced bythe radius rod.

A bifurcated pawl type of catch 32 engages automatically by the actionof a spring 33 over a pair of radial pins 34 on the free end of the legcylinder when the leg reaches its fully raised position. Remote controloperated means (now shown) is provided to actuate such catch against theinfluence of its spring means to release the leg so that the leg andwheel will fall by gravity about the hinge of the leg when theundercarriage is to be lowered.

The beforesaid locking plunger can operate the means for indicating tothe pilot that the leg is fully down, for which purpose the upper arm 6of the two arms of the radius rod can accommodate an axially slidableplunger 35 loaded in the opposite direction to the locking plunger l5 bya weak spring 38, one end of this indicator op- I crating plungerextending into the recess IS in the outer end of such inner arm 6 intowhich the locking plunger catch end 9 trips so that the locking plungerpresses the indicator operating plunger 35 upwards inside the radius rodas the locking action takes place. The other end of this indicatoroperating plunger passes through the top of the tubular part of the saidinner arm and is connected with a small crank 3'! pivoted between aforked inner end 6 of this arm 3, the pin of this crank carrying outsidesuch forked end an arm 38 carrying a, contact adapted to bridge contactsof a circuit closing device 39 connected to an electrically operatedindicator on the instrument panel of the aircraft.

Similarly to the arm '5, the upper arm --6 can be formed in two sectionsby making the knuckle joint end of the arm 6 from a strong metal sleeved3 threaded as at 44 into the tubular body part of the arm 6, the outerend of this sleeve being shaped to form a lug 45 to fit between thefurcations lfi of the arm I, such lug having the cam edge l'i formedthereon. The furcations i5 at the anchored or top end of the arm 6 can,as shown, comprise two plates bolted to a centre lug 6 of the arm 6, andbetween these furcations is located a pulley 46 rotating on a bolt 41,the cable 5 negotiating this pulley and another pulley 43 fitted aboutthe bearing member l2 of the pivot of the radius rod.

The pulley 46 is so located that the tensioned cable 5 extends alongsidethe radius rod clear of the knuckle joint.

In referring to the wheel carrying member I as a leg it will beunderstood that it may be of single axis tubular form as shown, aparallel pair of leg members or a frame unit adapted to support on or apair of wheels.

I claim:

In an aircraft retractable undercarriage, the combination of, a leghaving a wheel rotatably mounted on one end and having the other endadapted to be pivotally mounted on an aircraft, a straight foldablestrut having one end attached to said leg and the other end adapted tobe attached to the aircraft, said strut comprising two arms connected bymeans of a joint, spring-actuated means mounted on said strut forforcing the arms of said strut into co-a'xial' alignment a spring loadedpin slidably mounted in one of said arms and positioned to b projectedby said spring across said joint, a recess in said other arm positionedto receive said pin to lock said joint when said arms are in coaxialalignment, the other end of said plunger being connected to a lever andthe opposite end of said lever being connected to a cable arranged andpositioned to fold said strut, whereby when tension is applied to saidcable, said pin will be withdrawn and the joint unlocked just prior tothe folding of said strut.

JAMES MARTIN.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 1,329,533 IvIcCarroll Feb. 3,1920 2,277,896 Allbright Mar. 31, 1942 FOREIGN PATENTS Number CountryDate 473,202 Great Britain Oct. 3, 193'? 518,130 Great Britain Feb. 19,1940

